Preparation and readout of Majorana qubits in magnet-superconductor hybrid systems

Initializing the ground state of a quantum bit (qubit) based on Majorana zero modes is one of the most pressing issues for future topological quantum computers. We explore a protocol for initializing such topological qubits based on magnet-superconductor hybrid networks by coupling magnetic chains to a single molecule magnet. The parity of the Majorana state is converted to the presence or absence of a Yu--Shiba--Rusinov state at the molecule. The coupling can be activated by switching the spin state of the molecule, allowing the ground-state parity of the chain to be controlled. We demonstrate that initialization with either parity for a Majorana qubit can be achieved. We then introduce the augmented Majorana qubit, which includes the state of the molecule in the definition of the logical qubit. Using this definition we can initialize a qubit without high-precision timing.